This invention relates to fiber laser pump sources and, more particularly, to optical devices, such as fiber amplifiers and fiber lasers, which are pumped by the combined output of a plurality of fiber lasers.
In fiber optic telecommunications systems an information-bearing optical signal at one wavelength (.lambda..sub.s) is amplified by propagating it through a gain section of rare earth-doped fiber simultaneously with an optical pump signal of a different wavelength (.lambda..sub.p). The source of the pump signal is typically a solid state laser; e.g., a diode laser, a fiber laser, or a sapphire laser. In addition, multiple pump sources may be simultaneously coupled to the gain section. Although the use of multiple pump sources increases somewhat the complexity of the amplifier, it can serve several desirable purposes; e.g., to provide higher gain by coupling more optical power into the gain section than is possible or desirable from a single pump laser; to enable each of the pump lasers to be operated at a lower power level for a given amplifier gain, thereby extending the lifetime of the pump lasers and hence the reliability of the amplifier; and to provide redundancy in the event that one of the pump lasers were to fail.
Known schemes for coupling multiple pump lasers to a FAMP gain section include an arrangement which employs a pair of wavelength division multiplexers (WDMs)--one WDM couples a co-propagating pump signal from one pump laser to the gain section and the other couples a counter-propagating pump signal from the other laser to the gain section. In this arrangement, the pump lasers (typically diode lasers) have separate, non-overlapping resonators. See, for example, "Optical Fiber Amplifiers: Design and System Applications," A Bjarklev, Artech House, Inc., Boston-London 1993, p. 196, FIG. 8.2(a), which is incorporated herein by reference.